1. Field of the Invention
The present invention relates to a plasma display device and a method of driving a plasma display panel, and more particularly to a surface discharge alternating current driving type (surface discharge AC type) plasma display device and a method of driving a surface discharge AC type plasma display panel, having first and second representing units.
2. Description of the Related Art
Recently, a plasma display device has been practically adopted as a display device and adapted to various apparatuses and systems. A plasma display panel (PDP) is of a self-glowing type and can therefore display images in a well discernible manner. Moreover, the plasma display panel can offer a thin large screen and achieve fast display. The PDP is therefore attracting attention as a display panel taking over the CRT. In particular, a surface discharge AC type PDP is suitable for full-color display and therefore promising in the field of high-quality television. The surface discharge AC type PDP is highly requested to offer high image quality.
An approach to high-quality display images is to attain high definition, high-level gray scale, high luminance, low luminance for black display, or high contrast. High definition is attained by narrowing a pitch between pixels. High-level gray scale is attained by increasing the number of sub-frames (sub-fields) within a frame (field). High luminance is attained by increasing the number of times of sustaining discharge. Moreover, low luminance for black display is attained by minimizing an amount of glow to be emitted during a reset period. A PDP (surface discharge AC type PDP) is demanded to extend the service lives of phosphors and a protecting film and prevent sticking in a screen so as to prevent deterioration of quality of display images. There is also an increasing demand for a plasma display device and a method of driving a plasma display panel in which even when the same steady image is displayed for a long period, ordinary images will not be affected by sticking stemming from the steady image.
Incidentally, a plasma display device is used as display devices for various types of equipment, e.g., an automatic teller machine (ATM) to be installed at banks. In this case, a specified screen is kept displayed until a user (customer) uses the ATM. Even when the plasma display device is used as display devices for other various apparatuses, a specified steady screen may often have to be displayed continuously. When a specified screen is displayed continuously for a prolonged period of time, phosphors and a protecting film that are components of a PDP may deteriorate. Otherwise, sticking of the specified screen occurs in a screen.
Moreover, assume that an input picture is an ordinary-definition television picture consisting of 512 progressive scanning lines and conforming to the NTSC, PAL, or SECAM. In this case, it is unnecessary to switch the display lines. The parity signal is therefore not switched from one to the other. The same display lines remain lit. Assume that the same display lines are continuously lit, and that the display lines being lit are compared with those not lit. A difference in glowing efficiency of phosphors is larger than that observed when the display lines are alternately selected. Assume that the glowing efficiency of the phosphors on the display lines being lit is compared with that on the display lines not lit. In this case, the glowing efficiency of the phosphors on the display lines being lit is much poorer. This may cause shading in the direction of the lines.
Prior arts and the problems thereof will be explained later in connection with drawings.
An object of the present invention is to provide a plasma display device for distinguishing a steady image causing sticking from the other ordinary images by discriminating a representation by odd display lines from a representation by even display lines. In the plasma display device, sticking in a screen in which an ordinary image is displayed is indiscernible. Another object of the present invention is to provide a plasma display device capable of ensuring the extended service lives of phosphors and a protecting film and preventing sticking in a screen.
According to the present invention, there is provided a plasma display device including a first representing unit for lighting only one of even display lines and odd display lines which represent one frame, and a second representing unit for lighting only the other one of the even display lines and the odd display lines, comprising a judging unit for judging a condition for an image to be displayed; and a selector for selecting whichever of the first representing unit and the second representing unit is used to display an image, based on the results of judgment made by the judging unit.
When an image to be displayed is a steady image, the judging unit may use the first representing unit to display the image; and when an image to be displayed is any image other than the steady image, the judging unit may use the second representing unit to display the image. The steady image may be an initial operation image persisting until a predetermined operation is carried out, and images other than the steady image may be a plurality of images designated using the initial operation image. The judging unit may include a display time integrating unit for calculating a display time required by the image to be displayed by integrating time intervals during which the image is displayed, and the judging unit may switch an image display using the first representing unit and an image display using the second representing unit, based on the display time required by the image which is calculated by the display time integrating unit.
The judging unit may include an image comparing unit for detecting a change of the image to be displayed to another, and the judging unit may switch a first representation and a second representation, according to the detected change of the image. The comparing unit may compare the image to be displayed with an image stored in advance in a comparison image storage unit; when the image to be displayed agrees with the image stored in the comparison image storage unit, the first representing unit may be used to represent the image; and when the image to be displayed disagrees with the image stored in the comparison image storage unit, the second representing unit may be used to represent the image. After the image to be displayed is changed to another, if the steady image persists over a predetermined number of frames, the comparing unit may switch the first representation and the second representation.
The image display using the first representing unit and the image display using the second representing unit may be switched in response to an externally supplied switching signal. A first image may be displayed using both the first representing unit and second representing unit, and a second image may be displayed using one of the first representing unit and second representing unit. The first image may be a high-definition television picture, and the second image may be an ordinary-definition television picture. The plasma display device may light one of two display lines lying on and under each scan electrode, and may selectively light only the even display lines or the odd display lines.
Further, according to the present invention, there is provided a plasma display device including a first representing unit for lighting only one of even display lines and odd display lines which represent one frame, and a second representing unit for lighting only the other one of the even display lines and the odd display lines, wherein the first representing unit and the second representing unit represent mutually independent images.
According to the present invention, there is also provided a method of driving a plasma display panel that provides a first representation by lighting one of even display lines and odd display lines and a second representation by lighting the other one of the even display lines and the odd display lines, comprising the steps of judging a condition for an image to be displayed; and selecting whichever of the first representation and the second representation is used to display an image, based on results of the judgment.
When the image to be displayed is a steady image, the image may be displayed using the first representation; and when the image to be displayed is any image other than the steady image, the image may be displayed using the second representation. The steady image may be an initial operation image persisting until a predetermined operation is carried out, and the images other than the steady image may be a plurality of images to be designated using the initial operation image. A display time required by the image to be displayed may be calculated by integrating time intervals during which the image to be displayed is displayed, and the first representation and the second representation may be switched, based on the calculated display time. A change of the image to be displayed to another may be detected, and the first representation and second representation may be switched based on the detected change of the image to be displayed.
The image to be displayed may be compared with an image stored in advance in a comparison image storage unit; when the image to be displayed agrees with the image stored in the comparison image storage unit, the image may be displayed using the first representation; and when the image to be displayed disagrees with the image stored in the comparison image storage unit, the image may be displayed using the second representation. After the image to be displayed is changed to another, when a steady image persists over a predetermined number of frames, the first representation and the second representation may be switched.
The first representation and the second representation may be switched in response to an externally supplied switching signal. A first image may be displayed using both of the first representation and the second representation, and a second image may be displayed using one of the first representation and the second representation. The first image may be a high-definition television picture and the second image may be an ordinary-definition television picture. The plasma display panel may light one or the other of two display lines lying on and under each scan electrode, and may selectively light only the even display lines or the odd display lines.
Further, according to the present invention, there is also provided a method of driving a plasma display panel that provides a first representation by lighting one of even display lines and odd display lines that represent one frame, and a second representation by lighting the other one of the even display lines and the odd display lines, wherein the first representation and the second representation are used to display mutually independent images.